1. Field of the Invention
The present invention relates to a conveyance technique of a printing medium or the like.
2. Description of the Related Art
In recent years, a printing apparatus such as a copying machine or a printer is often used to print a photographic image. Especially, an inkjet printing apparatus can form an image of the same quality as a silver halide photo on the strength of reduction of the ink droplet size and improvement of image processing technologies.
Against the backdrop of the demand for higher image quality, a high accuracy is required to convey a printing medium. In particular, regarding a roller for conveying the printing medium, a very high accuracy is needed because the printing medium conveyance amount is almost proportional to the outer diameter of the roller. However, the accuracy of finishing of the roller is limited. Hence, there is a need of conveyance control capable of implementing a high conveyance accuracy regardless of a variation in the outer diameter of the roller or decentering of the roller.
In general, the main printing unit of the printing apparatus is formed from a printhead and a plurality of conveyance rollers provided on the upstream or downstream side of the printhead. In the printing apparatus having this arrangement, the conveyance amount upon switching the roller involved in conveyance is particularly problematic concerning the printing medium conveyance accuracy. For example, when switching from a state in which the printing medium is conveyed by two conveyance rollers on the upstream and downstream sides to a state in which the printing medium is conveyed only by the conveyance roller on the downstream side, the conveyance accuracy may lower due to the influence of the conveyance amount difference between the conveyance rollers. More specifically, bending that has occurred in the conveyance roller on the downstream side due to the conveyance amount difference between the conveyance rollers is released. This fluctuates the conveyance amount and lowers the image quality. To cope with this problem, Japanese Patent Laid-Open No. 2010-46994 proposes a method of correcting the conveyance amount in consideration of the influence of bending upon switching the conveyance state.
In the method of Japanese Patent Laid-Open No. 2010-46994, the influence of bending of the conveyance roller on the downstream side is corrected based on the conveyance amounts of the conveyance rollers at the time of switching the conveyance state. However, there exists a response delay of bending occurrence in the conveyance roller with respect to the conveyance amounts of the respective conveyance rollers. The image quality can further be improved by considering the response delay as well.